A hydraulic system uses a fluid under pressure to drive machinery or move mechanical components. In the aviation industry, virtually all aircraft make use of some hydraulically powered components. Depending upon the aircraft concerned, a single hydraulic system, or two or more hydraulic systems working together, may be used to power any or all of the following components: wheel brakes, nose wheel steering, landing gear retraction/extension, flaps and slats, thrust reversers, spoilers/speed brakes, flight control surfaces, cargo doors/loading ramps, windshield wipers, propeller pitch control. An aircraft hydraulic system will typically comprise the hydraulic fluid and three major mechanical components. Those components are the hydraulic pump which generates pressure, the hydraulically powered motor which powers the component (e.g., hydraulic actuator, hydraulic cylinder) concerned, and the system plumbing which contains and channels the fluid through the aircraft as required.
Several types of hydraulic pumps driven by a variety of power sources can be found in aviation applications. The pumps include gear pumps which are fixed displacement type pumps that move a specific amount of fluid per rotation, fixed displacement piston pumps which utilize a piston moving in a cylinder to pressurize fluid and move a specific amount of fluid with each stroke, and variable displacement pumps which are the most common types of pumps found on large aircrafts and can compensate for changes in the system demand by increasing/decreasing fluid output to maintain a near constant system pressure.
The motive power for these pumps has traditionally been generated by an engine; engine driven pumps are frequently mounted on the engine accessory gear box However, there is a trend in the aviation industry toward a more electrically based aircraft, e.g., replacing mechanical controls with electronic controls, to increase reliability, improve power quality, and reduce weight. The move to electronic controls allows for use of smaller and more efficient motors such as permanent magnet AC motors. The control of these electrical motors requires precise sensing and measurement of the angular rotor position of the motor to monitor and control velocity of the motor. Traditional position sensing methods have used various types of Hall effect sensors, resolvers, and encoders to provide a control-system usable angular position signal. This angular position signal/measurement has traditionally then been used with combinations of hardware and algorithms, or only algorithmic methods, to calculate velocity based on the change in angular measurement, e.g.,
            Δ      ⁢                          ⁢      position              Δ      ⁢                          ⁢      time        .However, current systems/methods for determining velocity have notable limitations. Some of these limitations include hardware-based methods that require expensive, decoder integrated circuits, hardware-based methods that increase parts count lowering MTBF (mean time between failures), and algorithmic-based methods whose design and implementation can add an undesired lag to the angular measurement which can result in reduced performance.